1. Field of Invention
This invention pertains to optical fiber switches for switching optical transmission paths. More particularly, this invention pertains to a fiber optic switch which can switch between incoming optical transmission paths based upon the quality or condition of the signal being transmitted.
2. Description of the Related Art
Optical fibers are commonly used for the transmission of all types of data, including telecommunications, video, and computer data. Fiber optic cables have become an alternative to conventional wire transmission. The advantages of fiber optic cables over wire include greater bandwidth over greater distances with less loss and less cost. Fiber optic cables are considerably less susceptible than metal conductors to unauthorized “taps” and eliminate RF problems and the need for electrical isolation interfaces such as isolators. Because of these advantages, fiber optic cables often are used as an alternative to wire in networks.
Typically, fiber optic cables are used to form a transmission line from an origination point to a destination point. Because of the great bandwidth of optical fiber, many times the fiber optic cable transmits in both directions, so that the origination point for one direction is also the destination point. Depending upon the length of the transmission line, lengths of fiber optic cable may have to be spliced, and the optical signal may have to be amplified in order to maintain the signal strength at the destination point. Along the transmission line, taps and routers may be used so that either portions of or all of the optical signal can be delivered to multiple destinations. Because of their widespread use, fiber optic networks oftentimes have complex topologies and numerous components, and accordingly, are subject to various faults. These faults may develop over a period of time and be evidenced by a slow degradation of signal quality and strength, as in dirt and grime accumulating at connection points and obstructing the cable's optical interface. Other faults may be catastrophic and occur suddenly, as in a cable being cut by an outside force or by failure of an upstream device.
U.S. Pat. No. 5,710,846, titled “Self-calibrating optical fiber switch,” issued to Wayman, et al., on Jan. 20, 1998, discloses a microprocessor controlled optical routing switch that samples the input signals and compares them to a reference calibration value. The switch disclosed in Wayman, et al., switches out an input when the sampled signal quality for that input degrades by an amount greater than a preset threshold value.
U.S. Pat. No. 5,726,788, titled “Dynamically Reconfigurable Optical Interface Device Using an Optically Switched Backplane,” issued to Fee, et al., on Mar. 10, 1998, discloses optical switches used in a dynamically reconfigurable optical telecommunications network. The switches disclosed in Fee, et al., are used for routing optical signals and are controlled by a microprocessor.
There is a need to provide fast, intelligent fault recovery when a fiber optic cable no longer carries a signal. Fault recovery needs to occur with little delay because with a great bandwidth, long out-of-service times result in the loss of a great amount of data and information.